It is widely known to use nitric oxide (NO) in a variety of applications. Next to technical applications such as an intermediate in the Ostwald process for the synthesis of nitric acid from ammonia, especially several therapeutic applications using nitric oxide are known.
One of the most famous therapeutic applications of nitric oxide is the administration for neonates suffering from Persistent Pulmonary Hypertension (PPHN). However, many comparable or other therapeutic applications are known and discussed for the use of nitric oxide. As an example, nitric oxide is used by the endothelium of blood vessels to signal the surrounding smooth muscle to relax, thus resulting in widening the blood vessels and therefore increasing blood flow. This leads to nitric oxide being particularly applicable for the therapy of hypertension. Further exemplary applications for nitric oxide are directed towards improving lung function and treating or preventing bronchoconstriction, reversible pulmonary vasoconstriction, for treating or preventing arterial restenosis resulting from excessive intimal hyperplasia, or for treating chronic obstructive pulmonary disease (COPD). Apart from that, the administration of nitric oxide is particularly useful for treatment of infected tissue e.g. to kill bacteria. This application mostly involves topical delivery of a source of nitric oxide containing gas to a skin surface containing infected tissue.
The storage of nitric oxide for example in containers, or gas cylinders, respectively, may however cause difficulties. Due to the fact that nitric oxide tends to react with oxygen, even minor impurities of oxygen in the stored gas may cause the formation of nitrogen oxides in higher oxidation states, in particular the formation of toxic nitrogen dioxide (NO2). Therefore, nitric oxide has only limited useful life time and may thus be stored only in a low concentration and for a limited time. For many applications, it is therefore preferred to generate nitric oxide in situ, i.e. directly before use.
The generation of nitric oxide may additionally lead to problems because of which several attempts to form nitric oxide are exercised.
Known from EP 1 903 003 A1 is a method and an arrangement for generating nitric oxide. According to this method, nitric oxide is generated by a photolytic cleavage of nitrite ions being present in a nitrite containing aqueous solution. In detail, an aqueous nitrite solution further comprising antioxidants is guided in a reaction chamber in which it is subjected to electromagnetic radiation for a defined period of time. Due to the influence of the radiation, the nitrite ion is cleaved, wherein nitric oxide is generated. The so generated nitric oxide may then be transported out of the reaction chamber by means of a carrier gas.
One of the major drawbacks of this known method for generating nitric oxide is the fact that under some circumstances, the concentration of the formed nitric oxide may not be kept completely constant over a long period of time.